PALAEOZOIC TIME. 413 



after the Carboniferous or Permian, that the rocks of the Urals 

 were folded and crystallized ; for Carboniferous rocks are flexed 

 and altered in the same manner as in the Appalachians. The 

 auriferous quartz veins probably date from this era. 



TRANSITION FROM THE PALEOZOIC TO THE MESOZOIC. 



The transition from Palaeozoic to Mesozoic time was strongly 

 marked in Geological history, — unequalled, in fact, by any of earlier 

 date after the Azoic revolution in which the Laurentian rocks were 

 folded and crystallized, and by any in later ages, with the single 

 exception of that from Mesozoic to Cenozoic time. The events 

 which give it this prominence are : — 



1. A thoroughly complete extermination of existing life.. 



2. An extinction of several great Palaeozoic races, the decline of 

 others, and a general change in the character of the life. 



3. The extensive folding and crystallizing of Palaeozoic formations 

 in many regions. 



4. The development of a number of prominent mountain-ranges, 

 making new features in the earth's topography. 



5. In North America, a great change in the scene of geological 

 progress, so that the regions are no longer the Eastern border, the 

 Appalachian, and the great Interior Continental; but, instead, the 

 Atlantic border, the Gulf border, and the Western Interior, or interior 

 west of the Mississippi. The Eastern Interior and the Appalachian 

 regions no longer participate in the rock-making. The three new 

 regions coalesce ; the last is but a continuation of the Gulf region 

 to the northwest over the area of the Rocky Mountains, which was 

 still low or submerged ; whether it communicated directly with the 

 Pacific is not ascertained. 



By the close of the Palaeozoic, nine-tenths of all the rocks of the 

 globe had been formed. During the epoch of revolution that fol- 

 lowed, these beds, besides undergoing in many regions an exten- 

 sive crystallization fitting them prospectively for the uses of art, 

 were also supplied with mineral wealth. Much of the gold of 

 the world comes originally from rocks which were metamor- 

 phosed and filled with veins at this time. The same is believed to 

 be true of platinum and diamonds. None of the precious metals 

 are yet known to occur in the crystalline Azoic. Some of the veins 

 of tin, copper, and lead, and mines of topaz, emerald, and sapphire, 

 are among the productions of this epoch of metamorphism. 



Thus furnished, the world was prepared for another stage in its 

 course of progress. 



